Coronary artery disease is the leading cause of death and disability in the major industrialized countries of the world. Treatment of advanced atherosclerotic coronary artery disease, beyond that amenable to therapy via medication alone, now generally includes interventional cardiology procedures in the form of Percutaneous Transluminal Coronary Angioplasty (PTCA) or cardiovascular surgery procedures in the form of Coronary Artery Bypass Grafting (GABG).
The PTCA technique involves the retrograde introduction from an artery in the leg or arm, of a catheter with a small dilating balloon at its tip. The catheter is advanced through the arteries by fluoroscopic guidance and is passed across the luminal narrowing of the coronary artery over a guide wire. Once in place, the catheter balloon is inflated for a short period of time. This results in mechanical deformation of the atherosclerotic plaque or the vessel wall with a subsequent increase in the cross-sectional area of the artery. This in turn reduces vessel obstruction and transluminal pressure gradients, and increases blood flow through the coronary artery.
PTCA or angioplasty is a term that now may include other percutaneous transluminal methods of decreasing stenosis within a coronary blood vessel besides balloon dilation alone. These methods include: lumen expansion with an endoluminal stent that prevents elastic recoil of the vessel; mechanical atherectomy with shaving, extraction, thermal ablation or ultrasonic pulverization of the lesion; and methods of endoluminal drug delivery or radiation treatment. Mechanical atherectomy may result in incomplete plaque removal, particularly in the side branch vessels of the artery, and/or embolization of plaque debris to the downstream coronary circulation. In addition, it is difficult, and sometimes impossible to provide complete coronary revascularization with PTCA techniques for patients with total vessel occlusions, long obstructions, or diffuse lesion sites. During the year 2000, approximately 1.4 million patients worldwide underwent PTCA procedures.
The CABG technique involves placing the patient on cardiopulmonary bypass (heart-lung machine), and temporarily stopping the heart muscle. Surgery is then affected on the coronary arteries in the form of bypass conduit vessels using vein or artery grafts from the aorta to the coronary artery distal to the lesion sites, thereby providing blood flow around the obstructions. Compared to PTCA procedures, CABG surgery provides more complete revascularization for patients with multi-vessel coronary artery disease. During the year 2000, it is estimated that 1 million patients underwent CABG surgery worldwide.
The profile of patients undergoing CABG surgery is continuously changing. Today, patients being referred for CABG surgery are older, and many have undergone previous revascularization procedures. Therefore, the number of patients having severe and diffuse coronary disease has been increasing. Diffuse multi-vessel coronary artery disease is a challenge for surgeons, precluding complete revascularization in some patients, while rendering others inoperable. Incomplete revascularization is one of the most important variables, affecting both operative and late mortality following CABG surgery. In particular, residual disease of the left anterior descending (LAD) artery has been shown to adversely affect patient survival. Recently, the application of new revascularization procedures, aimed at growing new coronary blood vessels using laser devices or angiogenesis drugs, has refocused attention on the surgical management of diffuse coronary artery disease. For patients with total vessel occlusions, long obstructions, or severe diffuse coronary disease, an endarterectomy procedure (removal of the atherosclerotic plaque) may be the only option that can produce good clinical results in otherwise inoperable situations.
Surgical endarterectomy of the right coronary artery (RCA) requires a different technique from that used for the LAD. The RCA and its atheromatous core are of a large caliber, thick, and strong. Further, the main RCA trunk and its major branches (the posterior descending and the posterolateral vessels) are in the same geometric plane. Therefore, RCA endarterectomy can usually be accomplished by the traction-counter-traction technique with or without mechanical assistance (i.e. gas dissection of the lesion from the vessel wall) through a relatively short vessel incision (arteriotomy).
In contrast, the LAD atheromatous core is narrow and delicate, and its thickness is usually uneven, being thicker and stronger near vessel bifurcations, and thinner in between the side branches, increasing the risk of plaque disruption under tension. Furthermore, the LAD artery has many branches that come off at two different geometric planes 90° apart (the septal and diagonal branches). When traction is applied to the atheromatous LAD core directed at extracting one set of branch vessels it exerts a sheering force on the other side branches, breaking the plaque off, and occluding the vessels (“snowplow effect”). Therefore, endarterectomy of the LAD artery should be done through a long arteriotomy incision that allows for the complete removal of atheromatous plaque from the main vessel and side branches under direct vision. Following endarterectomy, a vein patch is often required to close the artery before the distal bypass graft anastomosis can be performed.
Despite the major therapeutic advances in the treatment of coronary artery disease provided by PTCA interventions and CABG surgery, the long-term success of these procedures has been hampered by the development of vessel re-narrowing or re-closure. Abrupt vessel occlusion may develop during a period of hours to days post-procedure, due to vasospasm and/or thrombosis at the site of vessel injury. The most common and major limitation, however, is the development of progressive reversion of the diseased vessel to its previous stenotic condition, negating any gains achieved from the procedure. This gradual re-narrowing process is most commonly due to vessel constriction and/or to intimal hyperplasia, and is referred to as restenosis. Restenosis is generally believed to be a normal reparative response to endovascular injury after angioplasty, and in vein grafts following vessel bypass surgery. The sequence of events is similar for PTCA and CABG restenosis, progressing through the process of vasoconstriction, thrombus formation and organization, growth factor and cytokine release, and smooth muscle cell proliferation.
Clinical follow-up studies indicate that significant vessel restenosis occurs in about 40% of balloon angioplasty patients and in about 25% of the PTCA/stent patients within six months, and in about 20% of the CABG patients within one year. This complication of vessel restenosis results in increased patient morbidity, need for repeating the procedure, and escalating medical costs. With an estimated 2,400,000 PTCA and CABG procedures performed worldwide in 2000 for coronary artery revascularization, these percentages of restenosis mean as many as 640,000 patients may develop vessel restenosis within one year after operation. Thus, repeat procedures could account for over $9 billion in additional healthcare costs, which increase each year.
1. Field of the Invention
The present invention relates generally to methods and devices for performing coronary artery revascularization surgery. More specifically, it relates to methods and devices for repairing partially blocked coronary arteries, including the use of stents.
2. Description of Related Art
Coronary artery stents are known in the prior art. There are two broad groups of endocoronary stent devices: 1) balloon expandable and 2) self-expanding. Within these groups, there is substantial variability with regards to manufacturing techniques, materials, architecture, dimensions, surface coatings (i.e., drugs, radiation, or other biological material), and strut configurations. However, these stents, used only by cardiologists and not by cardiovascular surgeons, cannot be implanted in a coronary artery at the site of a major side branch vessel, because the stent may block or occlude the opening of the side branch vessel. Often the diseased area of a coronary artery is several centimeters in length, from which there are several side branch vessels, particularly for the LAD.
Drug delivery stents designed to inhibit stent thrombosis and intimal hyperplasia, termed restenosis, are known in the prior art. Drug delivery stents may not be completely effective, however, because of low tissue drug levels, drug washout into the blood stream, inflammatory response caused by the drug eluting coating, and increased stent dimensions due to coating thickness.
Thus, there is a need for improving the way coronary artery revascularization surgery is performed, that results in more complete and durable outcomes for patients, physicians, and healthcare delivery systems.